drm: rp1: rp1-dpi: Fix optional dependency on RP1_PIO

drivers/gpu/drm/rp1/rp1-dpi/Kconfig

@@ -7,5 +7,10 @@ config DRM_RP1_DPI
 	select DRM_VRAM_HELPER
 	select DRM_TTM
 	select DRM_TTM_HELPER
+	depends on RP1_PIO || !RP1_PIO
 	help
-	  Choose this option to enable Video Out on RP1
+	  Choose this option to enable DPI output on Raspberry Pi RP1
+
+	  There is an optional dependency on RP1_PIO, as the PIO block
+	  must be used to fix up interlaced sync. Interlaced DPI modes
+	  will be unavailable when RP1_PIO is not selected.

drivers/gpu/drm/rp1/rp1-dpi/rp1_dpi.c

@@ -217,12 +217,28 @@ static void rp1dpi_pipe_disable_vblank(struct drm_simple_display_pipe *pipe)
 		rp1dpi_hw_vblank_ctrl(dpi, 0);
 }
 
+static enum drm_mode_status rp1dpi_pipe_mode_valid(struct drm_simple_display_pipe *pipe,
+						   const struct drm_display_mode *mode)
+{
+#if !IS_REACHABLE(CONFIG_RP1_PIO)
+	if (mode->flags & DRM_MODE_FLAG_INTERLACE)
+		return MODE_NO_INTERLACE;
+#endif
+	if (mode->clock < 1000) /* 1 MHz */
+		return MODE_CLOCK_LOW;
+	if (mode->clock > 200000) /* 200 MHz */
+		return MODE_CLOCK_HIGH;
+
+	return MODE_OK;
+}
+
 static const struct drm_simple_display_pipe_funcs rp1dpi_pipe_funcs = {
 	.enable	    = rp1dpi_pipe_enable,
 	.update	    = rp1dpi_pipe_update,
 	.disable    = rp1dpi_pipe_disable,
 	.enable_vblank	= rp1dpi_pipe_enable_vblank,
 	.disable_vblank = rp1dpi_pipe_disable_vblank,
+	.mode_valid = rp1dpi_pipe_mode_valid,
 };
 
 static const struct drm_mode_config_funcs rp1dpi_mode_funcs = {

drivers/gpu/drm/rp1/rp1-dpi/rp1_dpi_pio.c

@@ -18,13 +18,16 @@
 #include <linux/kernel.h>
 #include <linux/errno.h>
 #include <linux/of.h>
-#include <linux/pio_rp1.h>
 #include <linux/pinctrl/consumer.h>
 #include <linux/platform_device.h>
 #include <drm/drm_print.h>
 
 #include "rp1_dpi.h"
 
+#if IS_REACHABLE(CONFIG_RP1_PIO)
+
+#include <linux/pio_rp1.h>
+
 /*
  * Start a PIO SM to generate an interrupt just after HSYNC onset, then another
  * after a fixed delay (during which we assume HSYNC will have been deasserted).
@@ -223,3 +226,16 @@ void rp1dpi_pio_stop(struct rp1_dpi *dpi)
 		dpi->pio = NULL;
 	}
 }
+
+#else /* !IS_REACHABLE(CONFIG_RP1_PIO) */
+
+int rp1dpi_pio_start(struct rp1_dpi *dpi, const struct drm_display_mode *mode)
+{
+	return -ENODEV;
+}
+
+void rp1dpi_pio_stop(struct rp1_dpi *dpi)
+{
+}
+
+#endif